Catalytic isomerization of 2-methyl-3-butenenitrile to linear pentenenitriles in the presence of certain metal salt and/or tri(hydrocarbyl)boron promoters

ABSTRACT

The present invention discloses the isomerization of 2-methyl-3butenenitrile to linear pentenenitriles in high yield by means of catalysts which comprise zero-valent nickel complexes promoted by certain metal salt and/or tri(hydrocarbyl)-boron promoters at temperatures in the range 10*-200* C. The linear pentenenitrile product, principally 3-pentenenitrile, is useful as an intermediate to adiponitrile.

Unite States Patent Chia [451 July 11, 1972 CATALYTIC ISOMERIZATION OF 2- METHYL-3-BUTENENITRILE TO LINEAR PENTENENITRILES IN THE PRESENCE OF CERTAIN METAL SALT AND/OR TRI(HYDROCARBYL)BORON PROMOTERS Inventor: Yuan-Tsan Chia, Wilmington, Del.

Assignee: E. I. du Pont de Nemours and Company,

Wilmington, Del.

Filed: June 29, 1970 Appl. No.: 50,907

a Related US. Application Data Continuation-impart of Ser. No. 758,578, Sept. 9, 1968, abandoned, which is a continuation-in-part of Ser. No. 678,216, Oct. 26, 1967, abandoned.

US. Cl ..260/465.9, 260/439 Int. Cl ..C07c 121/30 Field of Search ..260/465.9

Primary Examiner-Joseph P. Brust Att0rney-D.R.J. Boyd [57] ABSTRACT The present invention discloses the isomerization of 2-methy1- 3-butenenitri1e to linear pentenenitriles in high yield by means of catalysts which comprise zero-valent nickel complexes promoted by certain metal salt and/or tri(hydrocarbyl)-boron promoters at temperatures in the range 10200 C. The linear pentenenitrile product, principally 3-pentenenitrile, is useful as an intermediate to adiponitrile.

27 Claims, No Drawings CATALYTIC ISOMERIZATION OF 2-METIIYL-3- BUTENENITRILE TO LINEAR PENTENENITRILES IN THE PRESENCE OF CERTAIN METAL SALT AND/OR TRI(HYDROCARBYL)BORON PROMOTERS RELATED APPLICATION This application is a continuation-in-part of my copending application Ser. No. 758,578, filed Sept. 9, 1968, which is a continuation-in-part of my application Ser. No. 678,216 filed Oct. 26, 1967, both now abandoned.

FIELD OF THE INVENTION This invention relates to, and has as its principal object provision of, a new process for the catalytic isomerization of 2-methyl-3-butenenitrile to linear pentenenitriles.

BACKGROUND OF THE INVENTION The patent of Drinkard and Lindsey U.S. Pat. No. 3,496,215 issued Feb. 17, 1970 discloses and claims the hydrocyanation of certain olefinic compounds, which may include the starting material of this invention, 2-methyl-3-butenenitrile, and the principal product of this invention, 3-pentenenitrile, in the presence of zero-valent nickel catalysts which are effective as catalysts for isomerization of 2-methyl- S-butenenitrile by the process of this invention.

A continuation-in-part of the above-mentioned Drinkard and Lindsey Patent, Ser. No. 678,171, filed Oct. 26, 1967, now U.S. Pat. No. 3,536,748 discloses and claims the isomerization of 2-methyl-3-butenenitrile to linear pentenenitriles in the presence of the zero-valent nickel complex catalyst of its parent application. The present application covers an improvement in the process of the second Drinkard and Lindsey application.

There is no other known prior art which discloses isomerization of a branched chain pentenenitrile to a linear nitrile.

DESCRIPTION OF THE INVENTION It has now been found that the catalytic isomerization of 2- methyl-3-butenenitrile to pentenenitrile with certain nickel complex catalysts can be improved by the addition of certain promoters to the system.

The promoters employed in the present invention are salts of metals having atomic numbers 13, 2l32, 39-50 and 57 to 82 and compounds of the formula BR wherein R is an alkyl or an aryl radical of up to 18 carbon atoms. The mole ratio of promoter to catalyst should be in the range of 1:20 to 50:1.

The nickel catalysts which are employed in the present invention can be described broadly as zero-valent nickel complexes which are coordinated with at least one phosphorus ligand containing a POR linkage where R is alkyl or aryl of up to 18 carbon atoms, i.e., phosphorus ligands having the formula P(XYZ) where X is OR and Y and Z are OR or R and where any of X, Y and Z can be conjoined to form a divalent radical. Examples of divalent conjoined Y and Z are tetramethylene, pentamethylene, and ethylenedioxy groups. The ethylenedioxy group is an example ofa divalent conjoined X with Y or Z.

The preferred catalysts are zero-valent nickel compounds of the general formula Ni[P(XYZ)] and in particular those compounds where the P( XYZ) groups are aryl phosphites such as triphenyl phosphite and tricresyl phosphite.

In addition to the above tris(p-methoxyphenyl) phosphite. has been found to be a useful ligand with desirable solubility properties,

The catalyst can be prepared and added to the reaction mixture or alternatively the catalyst can be formed in situ by a number of techniques, for example, by reduction of a nickel salt in the presence of the phosphorus ligand. If sufficient ligand is present, the product will be zero-valent nickel compound as described above. On the other hand, the process of the present invention is operable when less than the stoichiometric amount of phosphorus ligand is present.

When a catalyst such as Ni[P(XYZ)] is employed, the process of this invention is believed to involve the attachment of a Z-methyI-S-butenenitrile molecule to the catalyst by displacement of two of the ligands. This or a similar intermediate may be formed directly where the catalyst is prepared in situ particularly when less than the stoichiometric quantity of the phosphorus ligand is employed. Rearrangement of the intermediate complex then occurs by migration of the nitrile group, although whether this occurs by an intermolecular or an intramolecular mechanism is not known. The promoters are believed to interact with the 'nitrile group and further facilitate the transformation. In some instances, as noted hereinafter, intermediate complexes having a structure which is not fully known can be obtained as solids from the reaction medium, which are stable and can themselves be employed as catalysts for the reaction.

It is apparent that the initial prepared catalyst and the complex formed by ligand displacement with the 2-methyl-3-butenenitrile molecule are zero-valent nickel complexes, however, the further intermediate states which may be present and be isolable in this system may or may not be complexes of zero-valent nickel, yet are capable of acting as catalysts. Zerovalent nickel compounds are believed to occur in the cycle regardless, and in any event some zero valent nickel compounds are believed to be present at all times in the system. Accordingly, in this specification and the appended claims, the term zero-valent nickel catalyst refers to the initial zerovalent nickel catalyst added to the system or formed therein and to intermediate catalytic species derived from such catalysts.

It is evident that mixtures of catalysts and/or promoters can be employed in the practice of this invention, and indeed are frequently inherently employed when the catalyst is formed in situ, especially when less than the stoichiometric amount of ligand necessary to form a zero-valent nickel compound is used.

The above definition of the zero-valent nickel compounds which are preformed catalysts in the practice of this invention includes species wherein mixtures of substituents on the phosphorus atoms or mixtures of ligands are used. It has been found that the use of such mixtures is frequently advantageous in preventing the crystallization of catalyst species from the reaction medium.

The preparation of zero-valent nickel compounds suitable as catalysts is disclosed in U.S. Pat. Nos. 3,152,158 and 3,328,443.

The nickel complex catalysts can also be prepared in situ by, for example, displacement of another neutral ligand with the required phosphorus ligand or by reduction of an Ni(ll) compound in the presence of the ligand.

The intermediate zero-valent nickel compounds which form active catalysts in situ prior to addition of the ligand can themselves be prepared in situ on addition of the ligand. Such nickel compounds, which include those containing carbon monoxide, phosphines, arsines, stibenes, arsenites, stibites, acrylonitrile, and mixtures thereof, can be represented by the formula:

wherein A, A A and A, are neutral ligands, which may be the same or different, and represent carbon monoxide and M(XYZ) wherein M is P, As, and Sb, and X, Y, and Z are the same or different and are defined as a member of the class consisting of R, NR' Cl, and F, and wherein R is a member of the class consisting of alkyl and aryl groups having up to 18 carbon atoms. When acrylonitrile is a neutral ligand, the values of A, A A, and A in the above formula are satisfied by two molecules of acrylonitrile alone (one molecule being represented by a pair of the As) or by two molecules of acrylonitrile and two M(XY'Z) entities (one molecule of acrylonitrile being represented by one of the A's).

The active catalyst is then prepared by addition of P(XYZ) ligand to the intermediate zero-valent nickel compound. The amount of phosphorus ligand relative to the intermediate nickel compound should provide at least one P(XYZ) group per nickel atom and preferably two moles per mole of nickel. A second technique involves adding the neutral phosphorus ligand (as defined above), a nickel (II) compound such as a nickel halide, e.g., NiCl Ni(CN) or Ni-bis(acetylacetonate) and a source of hydride (H') ions. Suitable sources of Hions are compounds of the structure M[BH H and MH, where M is an alkali metal or an alkaline earth metal and n is a number corresponding to the valence of the metal. Reduction can also be accomplished by use of an electropositive metal such as zinc. A third technique is to add dicyclopentadienylnickel and a neutral ligand such as P(OR") where R" is aryl, to the reaction mixture. In each case, the compound is formed under the displacement reaction conditions described above and no other special temperatures or pressures need be observed.

The intermediate zero-valent nickel compounds and also the zero-valent nickel catalysts and catalytic reaction products prepared in situ are characterized by having neutral ligands which are thought to be bonded to the central metal atom by both sigmaand pi-type bonds. This type of bonding is described, for example, in Cotton and Wilkinson (Advanced Inorganic Chemistry, lnterscience Publishers, 1962, pp. 602-606).

The improved isomerization process of the present invention requires the use of a promoter, which may be one or more members of the group comprising salts of metals belonging to Groups 18, 11B, IIIA, IIIB, IVA, IVB, VB, VIB VIIB, and VIII, i.e., elements of atomic number 13, 21-32, 39-50, and 57-82, of the Periodic Table, and tri(hydrocarbyl) borons. (The Periodic Table referred to here is, for example, that copyrighted in 1962 by the Dyna-Slide Co., and published by the E. H. Sargent and Co.) Preferred metals are those of Group IIB (Zn, Cd), VB (V), VIB (Cr, Mo), VIIB (Mn), and VIII (Fe, Co). The anions of the metal salts include halides (preferably chlorides or bromides), sulfates, phosphates and lower aliphatic carboxylates (preferably trifluoroacetates). The tri(hydrocarbyl)borons have the formula BR, in which R is a member of the class of alkyl and aryl hydrocarbon groups containing up to 18 carbon atoms. Triphenylboron is a preferred tri(hydrocarbyl)boron.

The amount of promoter generally is varied from about 1:20 to 50:1 molar ratio of promoter to catalyst. An amount in the molar ratio range of 1 :1 to 4:1 is preferred.

In some cases the promoter can be made in situ together with the catalyst. Thus the reduction of a nickel salt with zinc dust in the presence of a suitable phosphorus ligand produces zero-valent nickel compounds suitable for use as catalysts, and, simultaneously, zinc salts which act as promoters.

The process is normally carried out at atmospheric pressure and at any temperature in the range -200 C, preferably in the range 60l20 C. The pressure is not critical, however, and can be above or below atmospheric pressure if desired. Any of the conventional batch or continuous flow procedures may be used either in the liquid phase or in the vapor phase (with respect to the relatively volatile 2-methyl-3-butenenitrile reactant and linear pentenenitrile products). The reactor may be of any mechanically and chemically resistant material, and is usually of glass or an inert metal or alloy (e.g. nickel, copper, silver, gold, platinum, stainless steel, Monel, Hastelloy).

The process is usually carried out neat," i.e., without an added diluent or solvent. Any solvent or diluent that is nondestructive of the catalyst can also be used, however. Suitable solvents include aliphatic or aromatic hydrocarbons (hexane, cyclohexane, benzene), ethers (diethyl ether, tetrahydrofuran, dioxane, glycol dimethyl ether, anisole), esters (ethyl acetate, methyl benzoate), or nitriles (acetonitrile, hcnzonitrilc).

A nonoxidizing environment is desirable in order to retard deactivation of the catalyst. Accordingly, an inert atmosphere (e.g., nitrogen) is normally and preferably used although air may be used, if desired, at the expense of loss of a proportion of the catalyst through oxidation.

When the process is a typical batch operation in the liquid phase with or without a solvent, the catalytic nickel complex and the promoter are soluble to some extent at temperatures within the operable range and are usually completely soluble under the most preferred operating conditions.

When a hydrocarbon solvent as cyclohexane is used, the preformed or in situ-prepared promoted catalyst is generally fully dissolved until a temperature of about 50 C. is reached, at which point an insoluble material, usually orange to red in color, is formed which may remain undissolved as the isomerization reaction proceeds. It is believed that the colored material comprises a catalyst complex in which some of the 2- methyl-3-butenenitrile starting material is molecularly combined. The insoluble colored material can be separated from the reaction mixture, isolated as a solid and stored in an inert atmosphere. When such an isolated solid material is placed in contact with 2-methyl-3-butenenitrile it is an active isomerization catalyst under the conditions of the present process.

In a continuous flow procedure in the liquid phase the catalyst, promoter and excess ligand, if used, may all be coinponents of the flowing system. In a semi-vapor phase continuous operation the catalyst, metal salt and/or trihydrocarbyl/boron promoters and excess triaryl phosphite ligand, being essentially nonvolatile, may be in a mobile nonflowing liquid state. If preferred, the catalyst, promoter and nonvolatile excess ligand may be in a fixed bed on a solid support in a conventional flowing vapor phase operation.

The time element in the process is not critical, and may generally be governed by practical considerations. The time required for a practical level of conversion of 2-methyl-3-butenenitrile to linear pentenenitriles is dependent upon the temperature of reaction, i.e., operation at a lower temperature generally requires a longer time than operation at a higher temperature. A practical reaction time can be in the range of a few seconds to many hours, depending on the particular conditions and method of operation. It should be noted, however, that prolonged contact of the linear pentenenitrile product, consisting mainly of 3-pentenenitrile, with the promoted zerovalent nickel catalyst can result in gradual loss of 3-pentenenitrile by secondary rearrangement to 2-methyl-2-butenenitrile especially at higher reaction temperatures.

The molar ratio of 2-methyl-3-butenenitrile to catalyst is generally greater than 1:1, usually in the range from about 10:1 to 2000: 1, for a batch operation. However, it is usually in lower proportion, e.g., 1:2, for a continuous operation with a fixed-bed catalyst.

It is stated above that the related copending coassigned patent US. Pat. No. 3,496,215 discloses the catalytic zerovalent nickel complex of the present invention as it is used in effecting hydrocyanation of pentenenitriles, including 2- methyl-3-butenenitrile. In the presence of hydrogen cyanide the nickel complex preferentially catalyzes formation of a C saturated nitrile (2-methyl-glutaronitrile) from 2-methyl-3- butenenitrile, and though simultaneous rearrangement of 2- methyl-3-butenenitrile may seem possible in the light of the present invention, it is not obvious otherwise that contact of the catalyst with the branched chain pentenenitrile can result in rearrangement of the latter to a linear pentenenitrile. Because of the overriding competitive hydrocyanation reaction, in the practice of the present invention it is necessary to avoid the presence of large amounts of hydrogen cyanide, i.e., any amount of the order of or in excess ofa 1:] mole ratio with the 2-methyl-3-butenenitrile starting material. However, hydrogen cyanide has no significant effect per se on the isomerization reaction and its presence in minor amounts in the starting material can be tolerated if necessary. The isomerization process is preferably conducted in the absence of hydrogen cyanide.

In the isomerization process of converting 2-methyl-3-butenenitrile to linear pentenenitriles, the commercially practi-' cal objective is to obtain a maximum of linear pentenenitriles that can be converted to adiponitrile through later hydrocyanation. The related hydrocyanation art is exemplified in U.S. Pat. No. 3,496,217 and U.S. Pat. No. 3,492,218. In these patents, it is shown that the linear 3- and 4- pentenenitriles can be hydrocyanated to adiponitrile in high yield in the presence of zero-valent nickel catalysts. These same catalysts are used in the present isomerization process, which does not involve hydrocyanation. In order to reach an appreciation of the overall picture it is important to understand the dual role of the zero-valent nickel catalysts, i.e., their action as isomerization catalysts on the one hand and their action as hydrocyanation catalysts on the other. In the context of the present invention, the hydrocyanation role is recognized as being inoperative insofar as the preferred conditions of reaction are concerned. However, the hydrocyanation art is relevant because it discloses that the zero-valent nickel catalysts can control several distinct isomerizations among the possible different linear and branched chain pentenenitriles.

From the point of view of manufacturing intermediates to adiponitrilc, isomerization of 3-pentenenitrile to 4-pentcnenitrilc and of 2-methyl-3-butencnitrile to 3-pentenenitrile are desirable and even necessary. On the other hand, isomerizations of 3-pentenenitrile to Z-pentenenitrile or to 2- methyI-Z-butencnitrile are undesirable and unnecessary. On the basis of present understanding, the isomerization of 2- methyl-3-butenenitrile to 3-pentenenitrile in the presence of a zero-valent nickel catalyst is reversible, the equilibrium ratio of 3-pentenenitrile to 2-methyl-3-butenenitrile being about 94:6 at operable isomerization temperatures. Secondary isomerizations of 3-pentenenitrile in the presence of zerovalent nickel catalysts may go toward 4-pentenenitrile or toward 2-methyI-2-pentenenitrile. The preferred process of the present invention aids maximum primary isomerization of 2-methyl-3-butenenitrile to 3-pentenenitrile, does not inhibit desirable secondary isomerization of 3-pentenenitrile to 4- pentenenitrile and minimizes undesirable secondary isomeriation of 3-pentenenitrile to 2-methyl-2-pentenenitrile.

To prevent side reaction, it is sometimes advantageous to have an excess of P(XYZ) ligands present with respect to the nickel in the catalyst. The preferred excess ligands are the aryl phosphites wherein the aryl groups contain up to 18 carbon atoms. Generally, the excess ligands are present in at least a 2 molar excess as based on the nickel present. The only limit of excess ligands involves practical considerations. However, generally there is little advantage to be obtained in using over a 300-mole excess of ligand as based on 1 mole of nickel, since the rate of the displacement reaction becomes too slow to be practical due to the decreased concentration of nickel present. The excess ligands may be the same or different from the ligands attached to nickel in the initial nickel catalyst.

EMBODIMENTS OF THE INVENTION There follow some nonlimiting examples illustrative of the process of the present invention. In these examples, unless 6 otherwise noted, reaction pressures were autogenous. Other pressures are given in terms of mm. of mercury and temperature, in degrees Centigrade. Analyses were made by gas chromatography and the percentages are expressed in terms of area. Gas chromatographic data expressed in area percent are approximations of weight percent: see Purnell, Gas Chromatography,.lohn Wiley and Sons, 1962, page 275.

EXAMPLE I A. A 400-ml. stainless steel reactor was charged with 5.0 g. of tetrakis(triethyl ph0sphite)nickel(0), i.e., Ni[P(OC H,-,) l0 ml. of benzene and 10 ml. of a pentenenitrile fraction containing 84.7 percent 2-methyl-3-butenenitrile, 11 percent 3- pentenenitrile and 4.2 percent 2-methyl-2-butenenitrile. The reaction mixture was heated at 100 C. for 8 hours under autogenous pressure. The resultant liquid product (19.3 g.) was distilled under a pressure of 0.1 mm., the pot temperature being advanced gradually to 100 C. Distillate, 14.63 g., residue 3.22 g. Gas chromatographic analysis of the distillate showed it to contain 34 percent 2-methyl-3-butenenitrile, 13 percent 3-pentenenitrile, 52 percent Z-methyI-Z-butenenitrile and 0.4 percent 4-pentenenitrile.

B. A mixture of 5.0 g. of Ni[P(OC H;,),,| and 20 g. ofa pentenenitrile fraction containing 98.9 percent 2-methyl3-butenenitrile, 0.5 percent 2-methyl-2-butenenitrile and less than 0.1 percent S-pentenenitrile, charged under nitrogen, was heated at 100 C. for 2.5 hours. The crude product, analyzed by gas chromatography, contained 69.7 percent 2-methyl-3- butenenitrile, 26.9 percent 2-methyl-2-butenenitrile and 2.5 percent 3-pentenenitrile.

Example I is a control demonstrating the catalytic action of an unpromoted zero-valent nickel complex on the rearrangement of 2-methyl-3-butenenitrile.

EXAMPLES 2-65 The reactions described in these examples were conducted at atmospheric pressure in a 10 ml. 3-necked flask equipped with a condenser, thermocouple and rubber serum cap for withdrawing samples. The reactants were kept under an inert atmosphere throughout all stages. The reactor was charged with the nickel catalyst, promoter, if used, and the pentenenitrile starting material; the reaction mixture was stirred at room temperature; and in some instances an analytical sample was then withdrawn. The remaining reaction mixture was heated gradually to the reaction temperature and held there for the indicated time. The reaction mixture was then cooled to room temperature, and a sample was withdrawn for analysis by gas chromatography.

Table 1 represents the data for examples 2-65, which demonstrate the effect of various metal salts and of trihydrocarbyl boron as promoters for the zero-valent nickel catalyst rearrangement of 2-methyl-3-butenenitrile (2M-3 RN) to 3- and 4-pentenenitrile (3PN and 4-PN), i.e., the desired reaction of the invention. Catalyst A is shown by Vinal, et al., Inor. Chem. 3, I062 (I964) and Catalysts B, C and D by US. Pat. Nos. 3,152,158 and 3,328,443.

TABLE I Reactants Product, percent 2M-3BN b Mole ratio Temp., Time, Combined Example Catalyst 8 (g.) Promoter (g.) (pro/cat.) Percent Ml. 0. rs. 2M'3BN 3' and 4-PN ZnClz (0.032) 96. 3 2.0 3 95.1 ZnOlz (0.020) 99, 4 2, I) 120 2 98. 7 99. 0 2. 0 1 06. 6 0. 4 07. 6 2. 0 2 76. J 20. 0 ZllCIz (0.134) 1. 4/1 99. 1 2.0 26 2. 5 03. 1 0. 5 Z1101: (0.030) 1/1 96. 4 2.0 80 3 76. 0 5. 5 ZIICI: (0.030) l/l 90, 1 2.0 120 2 3. t) 51. 1 ZnClz (0.030) l/I U0. 4 2. 0 80 3 3|. 2 M. 3 ZIIUI: (0.040) l/l 00. 1 2. 75 120 2 0.0 an, I ZllClz (0.061) I/I 05. 2 i. (l 80 3 ll. l 83. t) ZnUl: (0.032) I/l 00. 2 .2. 0 s0 3 0. 3 x7. 0 Zntllz 0) V1 07. s 0. 0 120 2 0. 1 s7. s ZllClg (0.030) l/I 00,3 4 ll 80 3 75. M 20 I ZnOl: (0.031) H1 00. 3 2 0 s0 3 10,0 87. 7

1m l0l044 03H TABLE I--Contlnued Reaetants lrudut'l, port-0111.

11 10111111111) l1 111p., 'llnlv. (|11l1l111-1l Example Catalyst. (14.) Promoter (is) (pro/00L.) Ml. 1. hrs. 2M-3HN 3-1110! -1-lN 0 (0.323) 211011 (0.030) 1/1 00.3 2,0 110 3 17.3 711.7 17 C (0.324) 7.1101. (0.121) 4/1 003 2, 0 110 3 20.3 75,3 18 0 (0.327) 7.:101 (0.001) 2/1 00.3 2. 0 s0 3 25.9 7 0 0 (0.645) ZnClz (0.059) 1/1 00.3 2.0 3 7. '1 01.5 (0.045) ZuCl: (0.060) 1/1 07.0 4.0 120 2 0.5 37.0 (0.322) 211011 (0.060) 2/1 03.7 2. 0 120 2 5.1 33.7 (0.322) 211011 (0.119) 4/1 93.7 2. 0 120 2 5.7 00.3 (0.323) 211011 (0.032) 1/1 52.0 2.0 30 3 17.2 21.11 (0.321) 7.11011 (0.030) 1/1 45.3 2. 0 120 2 5.11 01,2 (0.331) Z1101: (0.030) 1/1 20.4 2.0 so 3 11.11 33.7 (0.322) ZnCl: (0.030) 1/1 5.3 2. 0 120 2 4, 0 02.4 (0.323) z11B1-1 (0.052) 1.1/1 00.3 2. 0 s0 3 10.0 77.5 (0.323) ZnBn (0.049) 1.1/1 99.4 2.0 120 2 7.3 07.4 (0.322) Z11SO1 (0.034) 1/1. 05 09.3 2.0 30 3 02.1 0.1 (0.333) Z1150. (0.035) 1/1.05 99.4 2.0 120 2 13.0 84.0 (0.323) Zn3(PO1)2 (0.086) 1/1 99.3 2.0 80 3 34.5 14.0 (0.356) Z11 (PO1)z (0 086) 1/1 99.4 2. 0 120 2 11.8 85. 1 (0.325) Zn(O1CCF1): (0 064) 1/1 96.3 2.0 80 3 59.1 25. 2 (0.327) Ln(0 0CF (0 003) 1/1 99.4 2.0 120 2 8.3 88.6 (0.322) 01101 (0.022) 1/1 99.3 2.0 80 3 88.7 10.4 (0.328) 0u01 (0.02 1/1 99.4 2.0 120 2 53.7 45.0 (0.322) CdCl2 (0.041) 1/1 99.3 2.0 80 3 88.6 10.3 (0.320) CdClz (0.040) 1/1 98.5 2.0 120 2 14.0 84.7 (0.327) AlCl; (0.028) 1/1 96.4 2.0 80 3 85.6 10.4 (0.320) A1011 (0.032) 1/1 99.2 2.0 120 2 59.2 36.2 (0.321) C0013 (0.054) 1/1 99.3 2.0 80 3 88.7 9.6 (0.3.7) 0501 (0.056) 1 1 99.4 2.0 120 2 14.3 83.9 (0.321) 51101: (0.043) 1/1 99.5 2.0 80 3 80.3 17.4 (0.327) 'IiC]; (0.035) 1/1 99.0 2.0 30 3 33.0 05.2 (0.322) 11(01 (0.072) 1/1 99.3 2.0 80 3 53.9 2.1 (0324) 1001. (0.070) 1/1 08.5 2.0 120 2 52.0 0.0 ((1.323) VCI) (0.035) 1/1 99.8 2. 0 80 3 94.1 5.3 (0.324) V011 (0.034) 1/1 99.1 2. 0 120 2 23.1 72.0 0.325 0101 (0.037) 1 1 99.3 2.0 80 3 52.7 40.7 0) 0101,. (0.035) 1/1 09.1 2. 0 120 2 38.5 53.2 4) 111001, (0.0314) 1/1 00.3 2. 0 s0 3 110.5 12. 0 4) M000 (0.030) 1/1 00.4 2. 0 120 2 0.0 37.7 I 3) M1100 (0.020) 1 1 06.4 2.0 80 3 112.0 13.0 1 2) M1101 (0.020) 1/1 00.2 2.0 120 2 23.0 73.0 (0.323) 1 0.01 (0.029) 1/1 00.4 2. 0 s0 3 40.5 40.1 0.323) 1 0.01 (0.023) 1/1 90.2 2. 0 120 2 7.0 33.2 (0.324) 1 0.01 (0.037) 1/1 90.4 2. 0 s0 3 80.7 11.5 (0.321;) 1 0.01 (0.035) 1/1 99.1 2.0 120 2 7.0 81.8 (0.321) 00011 (0.023) 1/1 99.7 2. 0 s0 3 3.3 01.2 (0.322) 0001 (0.029) 1/1 98.4 2.0 120 2 5.5 02.8 (0.322) N101. (0.020) 1/1 90.3 2.0 80 3 87.4 7. 0 (0.327) N101: (0.029) 1/1 93.4 2. 0 120 2 72.0 24. 9 (0.323 M01115): (0.054) 1 1 90.4 2.0 80 3 84.5 0.3 (0.322) B(C(1Hs)a (0.051) l/1 99.2 2.0 120 2 12.3 72.7 15 0 (0.324) B(n-C1H1)1(0.040) 1 1 98.8 2.0 so 3 94.0 4.2

0 Catalyst A was preformed tetrakis(triethy1 phosphite)nlcke1(0). Purity of the starting material in percent 2M-3BN is shown; balance N1[P(OC1H5)s]1; B, tetrakis(triphenyl pl1ospl1ite)niekel(0), N111 01 starting material includes 110 3- or 4-PN unless otherwise indicated. (0011119111; C, tetrakis(p-to1y1phosphite)niekel(0) Ni[P(OCaH1CH:):1]1; 9 Starting materials contained 3- and 4-PN as follows: Ex. 23, 46.0% and D, tetrakis(p-niethoyxplienyl phosphlte), NilP(OC(1H1OCH1):1]1. gPN; Ex. 24, 53.5% 3-PN; Ex. 25, 71.4% 3- and 4-PN; Ex. 26, 93.7%

EXAMPLES 66 and 67 67 120 2 6 0 90.5 2 9 67 120 5 5 2 89.6 4.3 The apparatus and procedure of Examples 2 to 65 were 7 12 2 5 8 7 1 used and analyt1cal samples were withdrawn over an extended per1od of time. The results demonstrate that time 1s not a cr1t1- cal factor 1n the process. It may be noted that the convers1on EXAMPLES 3- 5 of 2-methyl-3-butenen1tr1le (2M-3BN) to linear pentenemtrlles proceeded to a stablilized polnt at which the con- These examples demonstrate the zmc chlondewromoted cenirauon of 2M3BN was about 5 to 6 percent l that at rearrangement of 2-methyl-3-butenen1tr1le to lmear pen- 120 Fhere was a gradual l 4'PemenemPrleS tenemtnles 1n the necessary presence of a zero-valent mckel Compamed by a cwfespondmg gam m the of catalyst containing a tnaryl phosphlte ligand and prepared 1n me1h l-2-butenenmla (ZM-ZBN). The followlng Table nu. The procedure of Examples 2-67 was used and the appresents data for reactlon m1xturesconta1n1ng4.0 ml. of2M-3 paratus was the Same except in Examples 6942 which BN, 0.060-0.062 gram of ZnCl and 0.644-0.655 grams of ployed Sca]ed up equlpmem catalystc OfTable N'[P(OC6H4CH-1)3]4 The preparatlon of zero-valent mckel compounds used as startlng materlals in preparing the catalysts 1s shown by: Dub, TABLE ll Organometalhc Chemlstry, Vol. I, pp. 639-651, Sprmger-Verlag, lnc., New York l966) Examples -80 and Zeiss, Organometallic Chemistry, p. 484, Reinhold Publishing Corp., New York (1960) Examples 81, 82 and 84; and Malatesta T Tim P19111191 and Sacco, Ann. Chem. Rome 44, 134 (1954) Example 83. c a 70 The mole ratio of promoter to zero-valent nickel catal st C (MMJBN %3 and LPN MMJBN (where used) was 1:1 except in Examples 70, 76 and 79 (l:l.l),75 (l:l.4), 77 and 78(l:2)and 83 (122.4). (l 994 ln Examples 69-74, the zinc chloride is generated in situ, by

2 3 S reactlon of ZlflC dust with mckel chloride as the zcro-valent (.1. s0 24 5.1 04.0 07 75 nickel catalyst is formed. 07 0 9.2 0. The data for Examples 68-85 are presented in Table III.

TABLE III Reactants 2M-3BN Product. percent Ligand I Amount, 'lemp., Time, a Ex. Nickel compound [g.] radical (g.) Promoter (g.) Percent ml. C. hrs. 2M-3BN 3- and 4-PN 68 CBHB (0.278) Z1101: (0.030)... 99.3 2.0 120 2 99.4 0.0 69..-.. N101; [0.260] p-CuPhOCH; (3.24) Zn dust (0.13)... 98. 8 a 15. 68 110 2 41. 77 31. 7 70-.-. N101. 1.29 -o.H.cH. a.-19) Zn dust (0.6) =22. 09 109 (g- 11-... Niel. 1.3a 10.11.011.63 Zn dust (0.67) 22. 59 3-]; g 1a.-.. N101. 1.03 -onLoH. (11.12) Zn dust (0.521) 11.72 117 3. 2 1178 39159 73.-- N101: [0.030] H; (0.313) Zn dust (0.014).- 96.3 2. 0 80 3 93. 9 2. 3 74..." NlCli [0.030] CuHs (0.309) Zn dust (0.015).. 98. 6 2. 0 120 2 6. 0 91. 2 75--. N1(C5H )z [0.043] OuHs (0.284) ZnClz (0.029)..-. 99.8 2. 0 80 3 72. 4 26. 1 76 N1(C6H5)z [0.040] CoHs (0.276) Z1101: (0.032)-... 99.6 2.0 120 2 10.7 86. 6 77- C(iHs 0 H; (0.274) ZnClz (0.031).... 99.5 2.0. 80 3 97.0 2. 0

O fisNi NlCsHs (I3 CgHs 78..... (O H5Ni) (00)2[0.069] 0.11. (0.278) ZnCh (0.032)..-. 96.4 2. 0 so 3 95. o 0. 2 79..-.. (CtHQflP-Ifi-Cafls [0.090] C Hs (0.269) Z1101: (0.032)..-- 99. 5 2. 0 80 3 77. (i 20. 5

80 (CuH5)3PlTIi-C5H5 [0.102] 0 H; (0.276) ZnClg (0.032).... 99.8 2.0 80 3 99. 0 0

81..- [(CoHs)3P]zNi(C0)z [0.140] CgHs (0.275) Z1101: (0.030).... 99. 2 2. 0 120 2 02. 0 3. J 82..... CuH O\ 0 H; (0. 282) ZnCh (0.030).... 99. 1 2. 0 120 2 96. 8 l. 2

P Ni(C0): [0.162] (CaHs): 2

83....- [CsH50)aP sNi(C0) [0.227] CsHs (0.278; ZnClz (0.032) 99. 7 2. 0 80 99. l 0. 4 84--. [(CsHshAs 1N1(C0)z [0.161] CQH5 (0.276 ZnClz (0.031) 99. 1 2. 0 120 2 96. l 2. 4 85 C5H5N1)g(SCBH5)3 [0.104] CuHs (0.271) 21101; (0.030) 99. 7 2. 0 80 98. 7 0. 6

e The ligand has the formula. P(OR) in which R is the ligand radical. of starting material includes no 3- or 4-PN.

b Purity of the starting material in percent 2M-3BN is shown; balance EXAMPLE 86 The reaction was carried out at atmospheric pressure in-a ml 2-nccked flask equipped with a condenser and thermocouple, keeping the reactants under an inert atmosphere throughout all stages. The reactor was charged with 0.230 g. of zinc chloride, 1.366 g. of tetrakis(p-methoxyphenyl phosphite)nickel(0), 15 ml. of cyclohexane and 0.3 ml. of 99.8 percent 2-methyl-3-butenenitrile. The molar proportions in this mixture are 1:2:4 of Ni(0) compound:ZnCl,:nitrile. The reaction mixture was heated to 74 C., with stirring, and a red precipitate began formingat about 50 C. After 10 minutes at 74 C. the reaction mixture was filtered, using a hot funnel. The orange-red solid was collected in the funnel, removed and washed with small portions of hot cyclohexane. The washing and filtering operation was repeated five times, after which the solid was dried in vacuum for 40 hours, transferred into a vial and stored in a refrigerator kept inside an enclosure having maintained atmosphere of dry nitrogen.

A 2-ml. flask equipped with a condenser and a thermocouple was charged with 0.081 g. of the washed and dried orangered solid and 0.5 ml. of 99.8 percent Z-methyI-S-butenenitrile, all under a nitrogen atmosphere in a dry-box. The reaction mixture was stirred at room temperature, an orange-red solution was formed within a few minutes, and a sample of the solution promptly withdrawn for gas chromatographic analysis showed the presence of 2.8 percent t-3-pentenenitrile. The solution was then gradually heated, with stirring, to 80 C. and kept there for 3 hours. The solution was then cooled rapidly to room temperature and analyzed by gas chromatography with results showing the presence of 20.2 percent unchanged 2- methyl-3-butenenitrile and 78.9 percent of 3- and 4-pentenenitriles.

0-172 g. of zinc chloride, 1.208g. of tetrakis(p-tolyl phoss Grams.

phite)nickel(0), 15 ml. of cyclohexane and 0.3 ml. of 99.7 percent 2-methyl-3-butenenitrile [mole ratio NizZnznitrile l:l.5:4] were stirred and heated to C. for 15 minutes. The reaction mixtures were combined and then decanted, leaving a red precipitate which was washed 10 times with hot cyclohexane and dried under vacuum. A sample of the dried solid (0.081 g.) was dissolved in 0.5 ml. of 99.7 percent 2- methyl-S-butenenitrile, and the solution was heated at 80 C. for 2.7 hours. The cooled solution was analyzed by gas chromatography, which showed the presence of 67.3 percent of unchanged Z-methyI-S-butenenitrile and 31.0 percent of 3- and 4-pentenenitriles.

EXAMPLE 88 In the manner of Example 87, a dried red solid catalyst was prepared from 0.34 g. of zinc chloride, 2.134 g. of tetrakis(phenyl phosphite)nickel(0) and 0.6 ml. of 99.6 percent of 2-methyl-3-butenenitrile [mole ratio Ni:Zn:nitrile l:l.5:4[, reacted in 40 ml. of cyclohexane at 80-90 C. for about 4 hours. A sample of the solid catalyst (0.086 g.) was dissolved in 0.5 ml. of 99.6 percent of 2-methyl-3-butenenitrile, and the solution was heated at 80 C. for 3 hours. The resulting solution showed the presence of 43 percent unchanged 2-methyl-3-butenenitrile and 56 percent 3- and 4- pentenenitrile, by gas chromatographic analysis.

EXAMPLE 89 in the manner of Examples 2-65, a pair of runs were made with 2 ml. of 99.9 percent Z-methyI-S-butenenitrile and 0.187 g. of [(EtO),C,1-1 P],,Ni at 80 C. for 3 hours, one of the reaction mixtures also containing 0.030 g. of zinc chloride. Gas chromatographic analyses of the products showed that the mixture with zinc chloride contained 84.9 percent unchanged 2-methyI-3-butenenitrile and 7.3 percent 3- and 4-pentenenitrile, whereas the mixture without zinc chloride contained 98.4 percent and 1.2 percent of these components, respectively.

EXAMPLE 90 dilution. The starting material contained 2.88 percent 3-pen- A. The reaction was carried out at atmospheric pressure in a tenemmle' 25-ml. two-necked flask equipped with a condenser and thermocouple, keeping the reactants under an inert atmosphere EXAMPLES 97401 throughout all stages. The reactor was charged with 0.162 g. A series of catalytic isomerization reactions were run in of zinc dust, 0.327 g. of nickel chloride (NiCl 2.017 g. of small glass vessels thermostatted at 100 C. in each instance tris(p-methoxyphenyl) phosphite, 0.807 g. of 2-methyl-3-bu- 40 ml. of crude 2-methyl-3-butenenitrile were added and 40 tenenitrile and ml. of toluene. The molar proportions of mi. of a tetrakis tritolyl phosphite nickel catalyst solution with ZnzNicl zphosphiteznitrile in this mixture are 121:2:4. The 10 excess tritolyl phosphite were added, the mole ratio of nickel mixture was stirred, gradually heated to 80 C., and kept at to tritolyl phosphite being 4.3/1. Varying amounts of zinc this temperature for about 1 hour and 10 minutes. The reacchloride were used. Analyses of the liquids in weight percent tion mixture was then filtered while hot, giving an orange-red of components as determined by gas chromatography at the filtrate which was concentrated under vacuum at room temstart and at the end of the reactions are shown in Table V perature. The concentrated solution was placed in a refrigeratogether with the weights g.) of ZnCl used, the approximate tor located inside an enclosure (dry-box) having a maintained concentration of nickel in moles/liter in the solutions and the atmosphere of dry nitrogen. The chilled mixture was again 111- times required in minutes to achieve 85 percent conversion of tered, and the filtrate this time was evaporated to dryness 2-methyl-3-butenenitrile to 3 and4pentene nitriles.

TABLE V Analysis at start, Analysis at end,

wt. percent wt. percent Time Moles Ni for 85% ZnClz, 3- and 3- and per liter conversion Example gm. 2M3BN 4-PN 2M3BN 4-PN (approx) (minutes) under vacuum. The residual orange-red solid product was The linear pentenenitriles (3-pentenenitrile and 4-penplaced in a vial and stored in the refrigerator inside the drytenenitrile) obtained by means of the present invention are box. useful as intermediates to adiponitrile, which is a well-known B. Following the procedure of Example 86, 0.078 g. of the intermediate used in the production of commercial polyaorange-red solid and 0.51 ml. of 97.2 percent 2-methyl-3-bumides useful in the form of fibers, films and molded articles.

tenenitrile were mixed and heated to 80 C. for 3.08 hours. Since obvious modifications and equivalents in the inven- Gas chromatographic analysis of the reaction mixture showed tion will be evident to those skilled in the chemical arts, 1 the presence of 55.0 percent of unchanGed 2-methyl-3-bupropose t be bound solely by the appended claims.

mnenitrile and 42.2 er ent f 3-and 4- emen nitril The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: EXAMPLES 91'95 1. The process of isomerizing 2-methyl-3-butenenitrile and These examples, and also Examples 86-88 and 90, demonthereby producing a linear pentenenitrile which comprises strate the separation and isolation of solid zinc chloridecontacting said 2-methyl-3-butenenitrile, at a temperature promoted nickel-containing material from typical isomerizain the range of 10 to 200 C. with a promoted catalyst tion reaction mixtures containing at least one pentenenitrile. consisting essentially of:

These solid materials are shown to be active catalysts for the a. at least one zero-valent nickel complex catalyst having isomerization of 2-methyl-3-butenenitrile to 3- and 4-penat least one ligand consisting of tris(p-methoxypheny1) TABLE IV Example 91. 92 93 94 95 1.131 1.140. Mixed o, m and o-Tolyi (7.701). tolyl (3.539). p-tolyl (7.608). 2M-3BN (6.423 g.)... 2M-3BN (1.678 g.). 2M-3BN (1.593 g.) 3-PN (14.014 g.)... 3-PN (11.87 ml.). Solvent (ml) Cyclohexane(24) Cyclohexane (40) Cyclohexane (40) M01 ratio,Z P(OR) :RCN. 1:122:16 1:1:214 1:1:2:4 Tcmp., 8 80 Time, hours 2.24 (average) 5.59 (average) Part B:

Solid, g 0 080 2M-3BN, percent (ml.) Temperature, C 80 Time, hours Product, percent:

2M-3BN 3- and 4-PN Ligand formula is P(OR);, R being the ligand radical. Runs in section A in which solids were isolated from twin initial RCN is pentenenitrile: 2M-3BN being 2-methyl-3-butenenitrile, and runs and then combined prior to storage and testing. 3- and 4-PN being 3- and 4-pentenenitrile, respectively.

tenenitriles. The procedure of Example was used for Examphosphite or a ligand of the formula P(XYZ) wherein ples 91-95, and the data are presented in Table IV. X is OR and Y and Z are OR or R, R being an alkyl or EXAMPLE 96 aryl group of up to 18 carbon atoms, and wherein any 70 two of X, Y and Z can be conjoined to form a divalent A reaction flask was charged with 0.8 g. of Ni[(C H ),Sb], radical, and

(CO);, 0.14 ZnCl,,1.4G. of P(OC,H CH,),, and 25 ml. of 2- b. at least one promoter consisting of compounds of the methy1-3-butenenitrile. The mixture is maintained at C. formula 13R wherein each R' is an alkyl or aryl for 17 hours. Gas chromatographic analysis shows that the hydrocarbon group of up to 18 carbon atoms, or salts crude product contains 43.96 percent trans-3-pentenenitrile, 75 of metals of atomic number 13, 21-32, 39-50 and 1.37 percent cis-3-pentenenitrile, 0.09 percent trans-2-pen- 57-82, the mole ratio of promoter to catalyst being in tenenitrile and 1.50 percent 4-pentenenitrile, corrected for the range of 1:20 to 50:1.

2. The process of claim 1 wherein R is an aryl group.

3. The process of claim 1 wherein P(XYZ) is an aryl phosphite.

4. The process of claim 3 wherein the promoter is zinc chloride.

5. The process of claim 3 wherein the promoter is cadmium chloride.

6. The process of claim 3 wherein the promoter is nickel chloride.

7. The process of claim 3 wherein the promoter is copper chloride.

8. The process of claim 3 wherein the promoter is iron chloride.

9. The process of claim 3 wherein the promoter is cobalt chloride.

10. The process of claim 3 wherein the promoter is aluminum chloride.

11. The process of claim 3 wherein the promoter is triphenyl boron.

12. The process of claim 1 wherein the catalyst is prepared in situ.

13. The process of claim 1 wherein the catalyst is of a ligand consisting of tris(p-methoxyphenyl) phosphite or a ligand of the formula P(XYZ) wherein X is OR and Y and Z are R or OR wherein R is alkyl or aryl of up to 18 carbons and any of X, Y and Z can be conjoined to form a divalent radical, with an intermediate nickel compound of the formula in which A, A A and A are the same or different neutral ligands selected from a. carbon monoxide;

b. M(X'Y'Z) wherein M is P, Sb or As and X, Y and Z are the same or different and are R', NR' Cl and F, R being alkyl or aryl of up to 18 carbon atoms; and

c. acrylonitrile, two molecules of acrylonitrile satisfying either all of the As or only two of the As, in the latter case the other two As being satisfiled by M(X'Y'Z).

14. The process of claim 1 wherein the catalyst is formed by reduction of a nickel salt in the presence of a ligand consisting of tris(p-methoxyphenyl) phosphite or a ligand of the formula P(XYZ) in which X is OR and Y and Z are R or OR; R being an alkyl or aryl group of from 1 to 18 carbon atoms and any two of X, Y and Z can be conjoined to form a divalent radicalv 15. Process of claim 14 in which said nickel salt is a nickel halide which is reduced with zinc dust.

16. Process of claim 15 wherein R is an aryl group.

17. Process of claim 15 wherein P(XYZ) is a triaryl phosphite.

18. Process of claim 15 wherein the phosphorus ligand is tris(p-methoxyphenyl) phosphite.

19. In the process of isomerizing 2-methyl-3-butenenitrile to pentenenitrile with a zero-valent nickel catalyst having at least one ligand consisting of tris(p-methoxyphenyl) phosphite or a ligand of the formula P(XYZ) wherein X is OR and Y and Z are R or OR, R being an alkyl group or an aryl group of one to 18 carbon atoms and any two of X, Y and Z can be conjoined to form a divalent radical the improvement which comprises conducting said process in the presence of a promoter consisting essentially of BR when R is alkyl or aryl of one to 18 carbon atoms or salts of metals having atomic numbers 13, 21-32, 39-50, and 57-82 in a mole ratio of promoter to catalyst offrom 1:20 to 50: l.

20. The process of claim 19 in which said promoter is zinc chloride.

21. The process of claim 19 in which said promoter is cadmium chloride.

22. The process of claim 19 in which said promoter is nickel chloride.

23. The process of claim 19 in which said promoter is copper chloride.

24. The process of claim 19 in which said promoter is iron chloride.

25. The process of claim 19 in which said promoter is cobalt chloride.

26. The process of claim 19 in which said promoter is aluminum chloride.

27. The process of claim 19 in which said promoter is triphenyl boron. 

2. The process of claim 1 wherein R is an aryl group.
 3. The process of claim 1 wherein P(XYZ) is an aryl phosphite.
 4. The process of claim 3 wherein the promoter is zinc chloride.
 5. The process of claim 3 wherein the promoter is cadmium chloride.
 6. The process of claim 3 wherein the promoter is nickel chloride.
 7. The process of claim 3 wherein the promoter is copper chloride.
 8. The process of claim 3 wherein the promoter is iron chloride.
 9. The process of claim 3 wherein the promoter is cobalt chloride.
 10. The process of claim 3 wherein the promoter is aluminum chloride.
 11. The process of claim 3 wherein the promoter is triphenyl boron.
 12. The process of claim 1 wherein the catalyst is prepared in situ.
 13. The process of claim 1 wherein the catalyst is of a ligand consisting of tris(p-methoxyphenyl) phosphite or a ligand of the formula P(XYZ) wherein X is OR and Y and Z are R or OR wherein R is alkyl or aryl of up to 18 carbons and any of X, Y and Z can be conjoined to form a divalent radical, with an intermediate nickel compound of the formula in which A1, A2, A3 and A4 are the same or different neutral ligands selected from a. carbon monoxide; b. M(X''Y''Z'') wherein M is P, Sb or As and X'', Y'' and Z'' are the same or different and are R'', NR''2, Cl and F, R'' being alkyl or aryl of up to 18 carbon atoms; and c. acrylonitrile, two molecules of acrylonitrile satisfying either all of the A''s or only two of the A''s, in the latter case the other two A''s being satisfiled by M(X''Y''Z'').
 14. The process of claim 1 wherein the catalyst is formed by reduction of a nickel salt in the presence of a ligand consisting of tris(p-methoxyphenyl) phosphite or a ligand of the formula P(XYZ) in which X is OR and Y and Z are R or OR; R being an alkyl or aryl group of from 1 to 18 carbon atoms and any two of X, Y and Z can be conjoined to form a divalent radical.
 15. Process of claim 14 in which said nickel salt is a nickel halide which is reduced with zinc dust.
 16. Process of claim 15 wherein R is an aryl group.
 17. Process of claim 15 wherein P(XYZ) is a triaryl phosphite.
 18. Process of claim 15 wherein the phosphorus ligand is tris(p-methoxyphenyl) phosphite.
 19. In the process of isomerizing 2-methyl-3-butenenitrile to pentenenitrile with a zero-valent nickel catalyst having at least one ligand consisting of tris(p-methoxyphenyl) phosphite or a ligand of the formula P(XYZ) wherein X is OR and Y and Z are R or OR, R being an alkyl group or an aryl group of one to 18 carbon atoms and any two of X, Y and Z can be conjoined to form a divalent radical the improvement which comprises conducting said process in the presence of a promoter consisting essentially of BR''3 when R'' is alkyl or aryl of one to 18 carbon atoms or salts of metals having atomic numbers 13, 21-32, 39-50, and 57-82 in a mole ratio of promoter to catalyst of from 1:20 to 50:1.
 20. The process of claim 19 in which said promoter is zinc chloride.
 21. The process of claim 19 in which said promoter is cadmium chloride.
 22. The process of claim 19 in which said promoter is nickel chloride.
 23. The process of claim 19 in which said promoter is copper chloride.
 24. The process of claim 19 in which said promoter is iron chloride.
 25. The process of claim 19 in which said promoter is cobalt chloride.
 26. The process of claim 19 in which said promoter is aluminum chloride.
 27. The process of claim 19 in which said promoter is triphenyl boron. 